The long-term objectives of this grant have been to study the structure of immunoglobulis and to relate that structure at the level of amino acid sequences to certain membrane molecules, including the major histocompatibility antigens in mouse and man and the TL antigen in the mouse. Our perspective on this goal is to relate, through the data obtained on the primary protein structure, the evolutionary relationships of major molecules involved in the immune system, i.e. humoral antibody and cell surface components. During the year encompassed by this review, efforts have been made to upgrade the sensitivity of amino acid sequence analysis in this laboratory, to develop new approaches to automatic amino acid sequencing, to explore the possibility of utilization of 125I-PITC in place of 35S-PITC for microsequence techniques, and to evaluate solubilized cell surface components from murine lymphoblastoid cell lines. Special emphasis has been given to how the major histocompatibility anigens relate to viral structural proteins.